1. Technical Field
The present invention relates to a para-fully aromatic polyamide pulp, its preparing process and its preparing equipment, more particularly, the pulp is composed of micro fibrils having less than 1 .mu.m in its average diameter, and the pulp has a crushed oval shaped cross-section wherein the longest distance is at least 1.2 times than the shortest distance.
Also, the present invention relates to a process and apparatus for preparing the above pulp, more particulary, continuously orienting and maturing or orienting, maturing and cutting the pre-polymer (non-oreinted) that aromatic diamine-has been reacted with equivalent mole of aromatic diacid chloride in polymerization solvent.
Aromatic polyamide pulp is used as substitution of asbestos. It's usage are the substitution of asbestos in resin reinforcement, autoparts, gasket, pump packing, disk or drum brake, locomotive brake block, industrial brake, clutch facing, brake lining, friction material and construction material such as cement reinforcement.
Though each of the required properties in these adopted fields may differ. We take a more serious view in how much of the pulp is fibril and what is the length distribution of the fibrils. In case it is used as friction material, it is basically required to have excellent heat-resistance in order to endure heat generated from an instant friction. As it is used as packing or gasket, the restoration stability after compression is regarded important. This restoration stability is totally rely on the elasticity of pulp.
2. Description of the Related Art
Conventional preparing process of aromatic polyamide pulp and are examined in detail hereunder.
In U.S. Pat. No. 3,869,430, an aromatic polymer has been prepared by polymerizing an aromatic diamine and an aromatic diacid chloride in mixed solvent. One dissolves the resulting polymer in strong sulfuric acid to obtain a spinning liquid dope. One then extrudes it through a spinneret and finally coagulating it to prepare a filament. Normally, the preparing process of aromatic polyamide pulp is to cutting spinned filament, and refining in wet conditions to prepare a fibril developed aromatic polyamide pulp. In other word, develop fibril by damaging the surface of filament during refining process. As for the aromatic polyamide pulp prepared in this method, there has been a problem of limitation in pulp cross-section area. It is known that the spinned filament is normally 12 micrometer. The pulp cross-section obtained from cutting and refining of the aforesaid filament would have an almost round shape. Also, the cross-section area could not be more than that of original filament. When the pulp cross-section is round shaped, it has less contact area with resin than that of a crushed oval shape, and it's usability with resin will be lowered due to the low friction coefficient based on a jagged part.
As disclosed in U.S. Pat. No. 4,511,623, adds pyridine into the mixed polymerization solvent which polymerizes aromatic diamine with an aromatic diacid chioride, and then matures the polymer by leaving it 5 hours in normal temperature. One prepares polyamide pulp by grinding matured polymer. Even though this method makes it possibe to produce aromatic polyamide pulp without difficult and complicated spinning process, noxious pyridine has to be used in this method. At the same time, there is a process problem of polymer gellation during short time.
The pulp that has been prepared in this method, is composed of average diameter 2 .mu.m crushed oval shape fibril. The cross-section of pulp is a crushed oval shape akin to round, and both ends of pulp are needle shaped. Aforesaid "crushed oval shape akin to round" means the longest distance of cross-section is less 1.2 times than the shortest distance of cross-section. The cross-section of each fibrils, which form pulp, are crushed oval shaped and the longest distance of fibril surface is at least 1.2 times than the shortest distance of fibril surface. However, the cross-section of pulp, the aggregation of fibrils, is crushed oval shape akin to round.
As a result of this fact, the usability with resin would be improved due to increased contact with resin and lower friction coefficient of jagged parts than perfectly round shaped of pulp. But, the aforesaid effects would be less than perfectly crushed oval shaped of pulp. Consequently, heat transmission, heat proliferation, impact-resistance and dispersion, etc would be deteriorated in the end use.
In U.S. Pat. No. 5,028,372, one prepares a pre-polymer by reacting an aromatic diamine with an aromatic diacid chloride in a mixed solvent, and orienting the pre-polymer in multi-hole die. One cuts the pre-polymer after 2.about.8 minutes of maturing at 25.about.60.degree. C., and then matures the gel until it gets hard. After more than 90 minutes of maturing, shatters the hardened gel. maturing is performed in normal air or nitrogen air.
This preparing method was also a trial to eliminate the spinning process of dissolving polymer in sulfuric acid. In this method, however, a doubt of manufactural continuity has been brought up, and the property of pulp prepared in this method is remarkably lower than the property of pulp wherein pyridine was used as disclosed in U.S. Pat. No. 4,511,623. A report has been made that the pulp having these low properties can be used in an adopted field which apply the pulp obtained from filament.